This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Asses the PK, PD, safety and tolerability of RP103 compared to Cystagon in patients with nephropathic cystinosis. Patients taking Cystagon as part of their treatment for cystinosis will be enrolled into the study and results will be used to inform the design the confirmatory PK and pivotal PD study comparing RP103 to Cystagon.